Biological control potential of a laboratory selected generalist parasitoid versus a co-evolved specialist parasitoid against the invasive Drosophila suzukii

A few generations of laboratory selection can increase the developmental success of native parasitoids on invasive targets. However, for this approach to be used more widely for biological control, we need to understand if the improved performance of native species, achieved under artificial laboratory conditions, translates to improved control in more natural environments. It is also unknown what the biocontrol potential of laboratory selected generalist native parasitoids may be compared to co-evolved specialists that are typically introduced for biological control of invasive species. To assess how rearing in artificial diet affected host finding ability in natural hosts, we used laboratory selected (adapted) and nonadapted populations of the generalist native parasitoid Trichopria drosophilae to parasitize the invasive fly, Drosophila suzukii in three different fruit types. In a separate experiment, we compared the effectiveness of adapted and nonadapted populations of T. drosophilae in raspberries with a co-evolved specialist larval parasitoid Ganaspis brasiliensis from Asia that was recently approved for release in the USA. More adult parasitoids emerged in each fruit type of the adapted compared to the nonadapted population of T. drosophilae. D. suzukii emergence rates were reduced on average by 85% by the adapted T. drosophilae population indicating that the artificial rearing conditions did not significantly impair the ability of parasitoids to locate and attack hosts in natural hosts. The specialist G. brasiliensis had higher adult emergence than the adapted population of T. drosophilae; however, both parasitoid species were able to reduce D. suzukii populations to the same extent. These results show that despite the lower developmental success of the laboratory selected T. drosophilae, they killed the same proportion of D. suzukii as G. brasiliensis when host choice was restricted. In nature, where host choices are available, specialist and generalist parasitoids will be unlikely to exhibit the same biocontrol potential.